DETERMINATION OF RESONANCE FREQUENCIES AND VIBRATION CHARACTERISTICS OF STATORS HAVING ENCASED CONSTRUCTION
Girgis, Ramsis Sedhom
An accurate assessment of the resonance frequencies of stators is essential for designing a quiet electrical machine. Also, detailed information about the vibration characteristics of the stator is of much interest. In the newer construction of stators, the stator-core is encased tightly in the frame. This construction is considered to be simpler and more economical as it eliminates the use of ribs between the core and the frame. An analysis, of a general nature, for the determination of the various resonance frequencies and mode shapes of stators having encased construction is presented in the thesis. As the general frequency equation is derived on a three-dimensonal basis, it delivers information about not only the radial vibrations of the stator but also about torsional and axial vibrations. In addition, the flexural vibrations along the machine-length are taken into account in the analysis. The validity of the analysis is confirmed by experimental results which were obtained from the literature for stators of small as well as of large machines. A detailed study of the vibration characteristics of a representative stator is carried out and the results are presented in a generalized form. The advantages of the encased construction of stators over the conventional construction from the vibration considerations are discussed. Finally, the. validity of the simplified frequency equations which are derived from the general frequency equation, is checked.